With the reintroduction of street tramways (light railways) in the UK and the upgrading and extension of existing tram networks world wide, there is a continual need to improve products and methods of installation to keep in line with various installation requirements and to be able to compete within the market place.
It is no longer acceptable for tramlines to be noisy, cause vibration in surrounding structures or to damage the statutory undertaker pipes, cables or ducts due to corrosion from stray electrical currents running through the rails.
At present the method of fixing a rail into the street requires the following to be taken into account. Firstly, the rail must be held extremely securely in its correct position. Standardly, this is done by providing a track bed into which the rail line is positioned for fixing. This may cause difficulties in positioning the rail and maintaining that position while the rail is fixed into the street. Secondly, the method of fixing the rail must provide for reduction in both noise and vibration caused by the trams along the lines and also prevent any stray electrical current passing from the rail in to the neighbouring surroundings. Thirdly, because the rail lines are fixed into the street it is important that the method of fixing and the form of fixant used does not cause a hazard to other street users.
Many track bed construction methods are available to fix the rail into the correct position in the street but, many of these systems fail to fulfill the above mentioned requirements.
There are, however, two distinct methods which go part way to satisfying the requirements, namely a) provision of pre-vulcanised rubber sections that are fitted around the rail; and b) the use of liquid polyurethane rubber which is poured around a pre-installed rail to fully encapsulate the rail.
Although the pre-vulcanised rubber section method provides a lower installation cost the poured polymer method comes closer to fulfilling the requirements of rail line fixing.
The poured polymer system requires a concrete track slab to be formed into which two slots that hold the rails have been preformed. The track slab has to be formed very accurately as the position of the slots determines both the final vertical and horizontal alignment of the top of the rail. That alignment is also dependent on the roadways and streets surrounding the track slab, and this means that the positioning is an extremely difficult task. Variations in the slot width or depth results in the increase in the amount of polymer being used, hence cost.
For the system to work effectively the poured polymer must bond to the rail and the concrete slot. Before the polymer is applied, both substrates must be dry and therefore the entire working area must be protected from the wet weather.
It is possible with poured systems to add to the top layer of the polymer, i.e at the road surface, a variety of anti-skid materials e.g. bauxite or granite chippings. However, in order to prevent the heavier anti-skid materials from sinking into the polymer away from the surface, they have to be added in a separate top layer of polymer once the rest of the polymer has started to solidify.